EP0331737A1 - Photomagnetisches speichermedium - Google Patents

Photomagnetisches speichermedium Download PDF

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Publication number
EP0331737A1
EP0331737A1 EP88906911A EP88906911A EP0331737A1 EP 0331737 A1 EP0331737 A1 EP 0331737A1 EP 88906911 A EP88906911 A EP 88906911A EP 88906911 A EP88906911 A EP 88906911A EP 0331737 A1 EP0331737 A1 EP 0331737A1
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EP
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Prior art keywords
magnetooptical recording
film
atom
recording medium
magnetooptical
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EP88906911A
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English (en)
French (fr)
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EP0331737B1 (de
EP0331737A4 (en
Inventor
Kunihiko Mizumoto
Koichi Haruta
Hirokazu Kajiura
Koichi Igarashi
Hidehiko Hashimoto
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Mitsui Chemicals Inc
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Mitsui Petrochemical Industries Ltd
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Priority claimed from JP62198713A external-priority patent/JP2633572B2/ja
Priority claimed from JP62207629A external-priority patent/JPS6450256A/ja
Priority claimed from JP33555487A external-priority patent/JPH01179241A/ja
Application filed by Mitsui Petrochemical Industries Ltd filed Critical Mitsui Petrochemical Industries Ltd
Publication of EP0331737A1 publication Critical patent/EP0331737A1/de
Publication of EP0331737A4 publication Critical patent/EP0331737A4/en
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Publication of EP0331737B1 publication Critical patent/EP0331737B1/de
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10582—Record carriers characterised by the selection of the material or by the structure or form
    • G11B11/10586—Record carriers characterised by the selection of the material or by the structure or form characterised by the selection of the material
    • G11B11/10589—Details
    • G11B11/10591—Details for improving write-in properties, e.g. Curie-point temperature
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10582—Record carriers characterised by the selection of the material or by the structure or form
    • G11B11/10586—Record carriers characterised by the selection of the material or by the structure or form characterised by the selection of the material

Definitions

  • This invention relates to a magnetooptical recording medium having excellent resistance to oxidation and excellent magnetooptical recording characteristics. More particularly it relates to a magnetooptical recording medium comprising a substrate, a magnetooptical recording film and a reflection film, said films being laminated on said substrate in this order, having an easy axis of magnetization perpendicular to the film as well as excellent resistance to oxidation and excellent magnetooptical recording characteristics.
  • magnetooptical recording films comprising at least one transition metal such as iron, cobalt, etc., and at least one rare earth element such as terbium (Tb), gadolinium (Gd), etc., have an easy axis of magnetization perpendicular to the film and are capable of forming a small inverse magnetic domain with magnetization anti-parallel to the magnetization of the film.
  • Tb terbium
  • Gd gadolinium
  • magnetooptical recording films composed of such transition metals and rare earth elements as mentioned above there are disclosed those of Tb-Fe series containing 15-30 atom % of Tb, for example, in Japanese Patent Publication No. 20691/1982. There are also used magnetooptical recording films of Tb-Fe series to which a third component metal has been added. Furthermore, magnetooptical recording films of Tb-Co series, Tb-Fe-Co series and the like are known as well.
  • magnetooptical recording films have excellent recording reproducing characteristics, they still involve such a serious problem from a practical standpoint that they are subject to oxidation in the course of ordinary use thereof and their characteristics tend to change with the lapse of time.
  • pit corrosion is meant the occurrence of pinholes in the magnetooptical recording film. This corrosion proceeds mainly under the circumstances of high humidity, and it markedly proceeds, for example, in the recording films of such series as Tb-Fe, Tb-Co or the like.
  • a surface oxide layer is formed on the magnetooptical recording film, whereby the Kerr-rotation angle ⁇ k of the film changes with time and eventually comes to decrease.
  • Rare earth elements present in the magnetooptical recording film are selectively oxidized, thereby the coercive force Hc of the film comes to largely change with time.
  • Journal of the Society of Applied Magnetism of Japan cited above discloses an attempt to improve resistance to oxidation of magnetooptical recording films of Tb-Fe or Tb-Co series by incorporation into the films of such third component metal as Co, Ni, Pt, Al, Cr, Ti and Pd in an amount of up to 3.5 atom %.
  • said Journal reports that the incorporation of small amounts of Co, Ni and Pt into Tb-Fe or Tb-Co is effective in inhibiting the surface oxidation and pit corrosion of the resulting magnetooptical recording film but has no effect on inhibition of the selective oxidation of Tb contained as a rare earth element in this magnetooptical recording film.
  • This disclosure means that even if small amounts of Co, Ni and Pt are added to Tb-Fe or Tb-Co, Tb which is present in the resulting magnetooptical recording film is selectively oxidized, and the coercive force Hc of the film largely changes. Thus, even when small amounts up to 3.5 atom % of Co, Ni and Pt are added to Tb-Fe or Tb-Co, no sufficient improvement in resistance to oxidation of the resulting magnetooptical recording film is made.
  • Japanese Patent L-O-P Publn. No. 255546/1986 discloses a magnetooptical recording film comprising rare earth elements and transition metals which has been improved in resistance to oxidation by adding thereto such noble metal elements as Pt, Au, Ag, Ru, Rh, Pd, Os and Ir, within such a range that a Kerr-rotation angle necessary for regeneration of information recorded may be is retained.
  • Japanese Patent L-O-P Publn. No. 7806/1983 discloses a magnetooptical recording film comprising a polycrystalline thin film having a composition of PtCo in which Pt is contained in an amount of 10-30 atom %.
  • the above-mentioned polycrystalline thin film having this composition of PtCo involves such problems that said polycrystalline thin film as formed require heat treatment such as annealing because it is polycrystalline, that the polyrystalline grain boundaries frequently put out noise signals, and that it has a high Curie point.
  • the prior art magnetooptical recording films comprising Tb-Fe or Tb-Co and further incorporated with such third metal components as Co, Ni, Pt, Al, Cr, Ti and Pd, involve at least one of such problems that they are not sufficient in resistance to oxidation, small in C/N ratio and high in noise level, and that no high C/N ratio can be obtained unless a large bias magnetic field is applied (i.e. they are poor in bias magnetic field dependency).
  • a magnetooptical recording medium comprising (I) a magnetooptical recording film composed of (i) at least one 3d transition metal, (ii) from 5 to 30 atom % of at least one corrosion resistant metal and (iii) at least one rare earth element, and (II) a reflection film composed of a metal or alloy having a specified thermal conductivity, said films being laminated on a substrate.
  • the magnetooptical recording medium comprises a substrate, a magnetooptical recording film (I) and a reflection film (II), said films being laminated on said substrate in this order, said magnetooptical recording film (I) being a thin film of an amorphous alloy comprising (i) at least one 3d transition metal, (ii) from 5 to 30 atom % of at least one corrosion resistant metal and (iii) at least one rare earth element, and having an easy axis of magnetization perpendicular to the film plane, and said reflection film (ii) comprising a metal or alloy having a thermal conductivity of not higher than 2 J/cm.sec.K.
  • the magnetooptical recording medium which comprises a substrate, a magnetooptical recording film (I) comprising a thin film of an amorphous alloy having a composition specified above and a reflection film (II) comprising a metal or alloy having a thermal conductivity of not higher than 2 J/cm.sec.K., said films being laminated on a substrate in this order, has an excellent resistance to oxidation, and in consequence, it is advantageous in that its magnetooptical recording film (I) can be thin; a warp of the medium and film crackings are not liable to occur; it has a high C/N ratio; in addition to excellent magnetooptical characteristics, its coercive force and Kerr-rotation angle do not substantially change with time; and it has an increased reflectance.
  • Figs. 4 to 9 were obtained on magnetooptical recording media, each having a structure as shown in Fig.1 and comprising a substrate of an ethylene­cyclotetradodecene, a magnetooptical recording film of a thickness of 300 ⁇ and a reflection film of a nickel alloy having a thickness of 1000 ⁇ .
  • the magnetooptical recording medium 1 comprises a substrate, 2 such as a transparent disc, a magnetooptical recording film 3 and a reflection film 4, said films 3 and 4 being laminated on the substrate 2 in this order.
  • the magnetooptical recording medium 1 according to the invention may further comprise an enhancing film 5 between the substrate 2 and the magnetooptical recording film 3, as shown in Fig.2.
  • the magnetooptical recording medium 1 may comprise two enhancing films 5, one between the substrate 2 and the magnetooptical recording film 3 and the other between the magnetooptical recording film 3 and the reflection film 4.
  • the substrate 2 is preferably a transparent disc, which may be composed of an inorganic material such as glass or aluminium, or an organic material such as polymethyl methacrylate, polycarbonate, a polymer alloy of polycarbonate and polystyrene, amorphous polyolefins as described in US patent No,4,614,778, poly(4-methyl-1-­pentene), epoxy resins, polyethersulfone, polysulfone, polyetherimide and copolymers of ethylene and tetracyclododecene. Of these, copolymers of ethylene and tetracyclododecenes as described hereinafter are particularly preferred.
  • the substrate 2 is preferably composed of a random copolymer [A] of ethylene and at least one cycloolefin of the general formula [I] or [II], said copolymer having an intrinsic viscosity [ ⁇ ] of from 0.05 to 10 dl/g as measured in decalin at a temperature of 135 o C., and a softening temperature (TMA) of at least 70 o C.
  • TMA softening temperature
  • the component derived from the cycloolefins of the general formulas [I] and [II] is present in the form of recurring units as represented by the following general formulas [III] and [IV], respectively.
  • n and m each is 0 or a positive integer
  • l is an integer of at least 3
  • R1 through R12 each represents a hydrogen or halogen atom or a hydrocarbon group.
  • At least one cycloolefin selected from the group consisting of unsaturated monomers represented by the general formulas [I] and [II] is usable herein to copolymerize with ethylene.
  • the cycloolefins represented by the general formula [I] can easily be prepared by condensation of cyclopentadienes with appropriate olefins by Diels-Alder reaction, and similarly the cycloolefins represented by the general formula [II] can easily be prepared by condensation of cyclopentadienes with appropriate cycloolefins by Diels-Alder reaction.
  • the cycloolefins represented by the general formula [I] in the concrete are such compounds as exemplified in Table 1 or, in addition to 1,4,5,8-­dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, such octahydronaphthalenes as 2-methyl-1,4,5,8-dimethano-­1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-ethyl-1,4,5,8-­dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-propyl-­1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-hexyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-­octahydronaphthalene, 2,3-dimethyl-1,4,5,8-d
  • cycloolefins represented by the general formula [II] in the concrete are, for example, those as exemplified in Tables 3 and 4.
  • the random copolymer [A] comprises a first component derived from ethylene and a second component derived from at least one cycloolefin of the general formula [I] or [II], as the essential constituent components, if desired, it may further comprise a third component derived from at least one other copolymerization monomer in an amount of up to an equimolar to that of the first component contained in the copolymer.
  • Monomers which can be used to form the third component include, for example, alpha-olefins having from 3 to 20 carbons atoms such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-­hexadecene, 1-octadecene and 1-eicocene.
  • alpha-olefins having from 3 to 20 carbons atoms such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-­hexadecene, 1-octadecene and 1-eicocene.
  • the recurring units (a) derived from ethylene are present in an amount of from 40 to 85 % by mole, preferably from 50 to 75 % by mole, while the recurring units (b) of the general formula [III] or [IV] derived from the cycloolefin or cycloolefins are present in an amount of from 15 to 60 % by mole, preferably from 25 to 50 % by mole, and these recurring units (a) and (b) are arranged in the copolymer [A] substantially at random.
  • the molar percentage of the recurring units (a) and (b) were determined by 13C-NMR. The fact that the copolymer [A] is completely soluble in decalin at a temperature of 135 o C., indicates that it is substantially linear and free from a gel-forming cross-­linked structure.
  • the copolymer [A] has an intrinsic viscosity [ ⁇ ] of from 0.05 to 10 dl/g, preferably form 0.08 to 5 dl/g, as measured in decalin at a temperature of 135 o C.
  • the softening temperature (TMA) of the copolymer [A], as measured by a thermal mechanical analyzer is at least 70 o C., preferably from 90 o to 250 o C., and more preferably from 100 o to 200 o C.
  • the softening temperature (TMA) of the copolymer [A] was determined by monitoring thermal deformation behavior of a 1 mm sheet of the copolymer [A] using a thermomechanical analyzer supplied by Du pont. More specifically, a quarz needle was vertically placed on the sheet under a load of 49 g and the assembly was heated at a rate of 5 o C./min. The temperature at which the needle penetrated into the sheet by a depth of 0.635mm was taken as the softening temperature of the copolymer [A].
  • the copolymer [A] has a glass transition temperature (Tg) of normally from 50 o to 230 o C, and preferably from 70 o to 210 o C.
  • the crystallinity of the copolymer [A], as measured by X-ray diffractomery is normally from 0 to 10 %, preferably from 0 to 7 %, and more preferably from 0 to 5 %.
  • the magnetooptical recording film 3 comprises (i) at least one 3d transition metal, (ii) at least one corrosion resistant metal and (iii) at least one rare earth element.
  • the 3d transition metal (i) use is made of Fe, Co, Ti, V, Cr, Mn, Ni, Cu, and Zn, alone or in combination. Of these, Fe, or Co or both Fe and Co are particularly preferred.
  • the 3d transition metal is present in the magnetooptical recording film 3 in an amount of preferably from 20 to 90 atom %, more particularly from 30 to 85 atom %, and the most preferably from 35 to 80 atom %.
  • the corrosion resistant metal (ii) incorporated into the magnetooptical recording film 3 is effective to enhance the resistance to oxidation of the film.
  • the corrosion resistant metal use is made of Pt, Pd, Ti, and Zr, alone or in combination.
  • Pt, Pd and Ti are preferably used alone or in combination.
  • Pt and Pd are preferably used alone or in combination.
  • the corrosion resistant metal is present in the magnetooptical recording film 3 in an amount of from 5 to 30 atom %, preferably from 5 to 25 atom %, more preferably from 10 to 25 atom %, and the most preferably from 10 to 20 atom %.
  • the resistance of the magnetooptical recording film to oxidation is not appreciably improved, and thus, the coercive force of the film tends to greatly change with time, or the Kerr-rotation angle of the film tends to decrease, or the reflectance R of the film tends to be inferior to that of the corresponding film with no added Pt or Pd.
  • the content of the corrosion resistant metal of the magnetooptical recordingmedium is in excess of 30 atom %, the Curie point of the film tends to be unduly reduced and frequently becomes lower than ambient temperature.
  • the magnetooptical recording film 3 contains at least one rare earth element selected from Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, La, Ce, Pr, Nd, Pm, Sm and Eu. Of these, Gd, Tb, Dy, Ho, Nd, Sm and Pr are preferred.
  • the rare earth element is present in the magnetooptical recording film 3 in an amount of preferably from 5 to 50 atom %, more preferably from 8 to 45 atom %, and the most preferably from 10 to 40 atom %.
  • the magnetooptical recording film (I) preferably has the following composition.
  • Fe or Co or both are contained, and Fe and/or Co is preferably present in the magnetooptical recording film in an amount of at least 40 atom % but not more than 80 atom %, preferably at least 40 atom % but less than 75 atom %, and more preferably at least 40 atom % but not more than 59 atom %.
  • Fe and/or Co present in the magnetooptical recording film is preferably in such an amount that the Co/(Fe + Co) ratio by atom is from 0 to 0.3, preferably from 0 to 0.2, and more preferably from 0.01 to 0.2.
  • the amount of Fe and/or Co is in the range of at least 40 atom % but not more than 80 atom %, there is such an advantage that a magnetooptical recording film which is excellent in resistance to oxidation and has an easy axis of magnetization perpendicular to the film is obtained.
  • the recording sensitivity of the magnetooptical recording film can be adjusted by the amount of Co to be incorporated and, moreover, a carrier level of reproduced signal increases by incorporating Co.
  • the Co/(Fe + Co) ratio by atom is from 0 to 0.3, preferably from 0 to 0.2, and more preferably from 0.01 to 0.2.
  • Fig. 4 shows a relationship between the Co/(Fe + Co) ratio by atom and the noise level in dBm on a magnetooptical recording film of PtTbFeCo series
  • Fig. 5 shows a relationship between the Co/(Fe + Co) ratio by atom and the noise level in dBm on a magnetooptical recording film of PdTbFeCo series.
  • Fig. 6 shows a relationship between the erasion deterioration in terms of ⁇ C/N ratio in dB and the Co/(Fe + Co) ratio by atom on two series of magnetooptical recording films, one of the compostion of PtTbFeCo and the other of the composition of PdTbFeCo.
  • Preferred magnetooptical recording films contain Pt or Pd, or both, as a corrosion resistant metal, and the amount of Pt and/or Pd contained in the prefered magnetooptical recording films is from 5 to 30 atom %, preferably more than 10 atom % but not more than 30 atom %, more preferably more than 10 atom % but less than 20 atom %, and the most preferably at least 11 atom % but not more than 19 atom %.
  • the presence in the magnetooptical recording film of Pt and/or Pd in an amount of at least 5 atom %, particularly in excess of 10 atom % brings about such advantages that resistance to oxidation of said recording film becomes excellent, and even when it is used for a prolonged period of time, no pit corrosion occurs and the C/N ratio does not become low.
  • Fig. 7 shows a relationship between the content of Pt or Pd in the magnetooptical recording film containing Pt or Pd and the decrease of the C/N ratio when said recording film is retained for 1000 hours under the circumstances of 85% RH and 80 o C.
  • a magnetooptical recording film having a composition represented by Pt13Tb28Fe50Co9 or Pd12Tb28Fe53Co7 will not change in the C/N ratio at all even when it is retained under the circumstance of 85% RH and 80 o C for 1000 hours.
  • a magnetooptical recording film having a composition represented by Tb25Fe68Co7 containing no Pt or Pd will greatly decrease in the C/N ratio when it is retained for 1000 hours under the circumstances of 85% RH and 80 o C.
  • a sufficiently high C/N ratio can be obtained even by a small bias magnetic field when information is recorded on the magnetooptical recording film or when the information recorded is read out therefrom. If a sufficiently high C/N ratio is obtained by a small bias magnetic field, a magnet for producing a bias magnetic field can be made small in size and, moreover, heat generation from the magnet can be inhibited and hence simplification of a driving device for an optical disc bearing the magnetooptical recording film thereon is made possible. Moreover, because a sufficiently large C/N ratio is obtained by a small bias magnetic field, it becomes easy to design a magnet for magnetic field modulation recording capable of overwrite.
  • Fig. 8 shows a relationship between the bias magnetic field and the C/N ratio (dB) of a magnetooptical recording film having a recommended composition of Pt13Tb28Fe50Co9 and of a magnetooptical recording film having a composition represented by Tb25Fe68Co7.
  • Fig. 9 shows a relationship between the content of Pt or Pd and the minimum bias magnetic field (Hsat, (Oe) ) on a magnetooptical recording film of PtTbFeCo series and on a magnetooptical recording film of PdTbFeCo series.
  • At least one rare earth element is contained, and usable as the rare earth element is Nd, Sm, Pr, Ce, Eu, Gd, Tb, Dy and Ho, alone or in combination.
  • rare earth elements preferably usable are Nd, Pr, Gd, Tb and Dy, and particularly preferred is Tb.
  • the rare earth elements may be used in combination of two or more, and in this case the combination preferably contains at least 50 atom % of Tb.
  • this rare earth element is present in a magnetooptical recording film in such an amount as 0.15 ⁇ x ⁇ 0.45, preferably 0.20 ⁇ x ⁇ 0.4, wherein x represents RE/(RE + FE + Co) [atomic ratio].
  • Examples of useful elements for this purpose other than those constituents of the magnetooptical recording film include such elements as mentioned below.
  • transition elements include Sc, Ti, V, Cr, Mn, Ni, Cu and Zn.
  • transition elements include Y, Zr, Nb, Mo, Tc, Ru, Rh, Ag and Cd.
  • transition elements preferably used are Zr and Nb.
  • transition elements include Hf, Ta, W, Re, Os, Ir, Au and Hg.
  • transition elements preferably used is Ta.
  • B, Al, Ga, In, and Tl are used.
  • C, Si, Ge, Sn and Pb are used.
  • N, P, As, Sb and Bi are used.
  • Te preferably used is Te.
  • the magnetooptical recording films having a composition described above have an easy axis of magnetization perpendicular to the film plane and that many of them may be an amorphous thin film which exhibits a Kerr hysteresis of a good angular loop, indicating that it is perpendicularly magnetizable and capable of magnetooptical recording.
  • Kerr hysteresis of a good angular loop used herein we mean that the ratio ⁇ k2/ ⁇ k1 is at least 0.8 wherein ⁇ k1 is a saturated Kerr-rotation angle that is a Kerr-rotation angle where the external magnetic field is maximum, and ⁇ k2 is a residual Kerr-rotation angle that is a Kerr-rotation angle where the external magnetic field is zero.
  • the magnetooptical recording film 3 preferably has such a thickness that it has a light transmission of at least 5 % in the absence of the reflection film 4.
  • the thickness of the magnetooptical recording film 3 is normally from 100 to 600 ⁇ , preferably from 100 to 400 ⁇ , and more preferably from 150 to 300 ⁇ .
  • the magnetooptical recording medium 1 according to the invention is provided with a reflection film 4 on the magnetooptical recording film 3.
  • the reflection film 4 is composed of a metal or alloy having a thermal conductivity of not higher than 2 J/cm.sec.K, preferably not higher than 1 J/cm.sec.K.
  • the reflection film 4 is composed of a metal or alloy having a reflectance of at least 50 %, preferably at least 70 %, and a thermal conductivity of not higher than 2J/cm.sec.K, preferably not higher than 1 J/cm.sec.K.
  • Suitable materials for constituting the reflection film 4 include, for example, Pt having a thermal conductivity of 0.71 J/cm.sec.K., Pd having a thermal conductivity of 0.76 J/cm.sec.K., Ti having a thermal conductivity of 0.71 J/cm.sec.K., Co having a thermal conductivity of 0.99 J/cm.sec.K., and Zr having a thermal conductivity of 0.23 J/cm.sec.K., and alloys thereof.
  • the reflection film 4 is composed of a nickel alloy having a reflectance of at least 50 %, preferably at least 70 %, and a thermal conductivity of not higher than 2 J/cm.sec.K, preferably not higher than 1 J/cm.sec.K.
  • Suitable nickel alloys for constituting the reflection film 4 preferably comprise nickel as the primary component and at least one alloying metal selected from the group consisting of silicon, molybdenum, iron, chromium and copper.
  • Such nickel alloys contain nickel in an amount of from 30 to 99 atom %, preferably from 50 to 90 atom %.
  • nickel alloys usable herein to constitute the reflection film include, for example, Ni-Cr alloys (for example, an alloy of 30-99 atom % of Ni and 1-70 atom % of Cr, preferably an alloy of 70-95 atom % of Ni and 5-30 atom % of Cr), Ni-Si alloys (for example, an alloy of 85 atom % of Ni, 10 atom % of Si, 3 atom % of Cu and 2 atom % of Al).
  • Ni-Cu alloys for example, an alloy of 63 atom % of Ni, 29-30 atom % of Cu, 0.9-2 atom % of Fe, 0.1-4 atom % of Si and 0-2.75 atom % of Al).
  • Ni-Mo-Fe alloys for example, an alloy of 60-65 atom % of Ni, 25-35 atom % of Mo and 5 atom % of Fe.
  • Ni-Mo-Fe-Cr alloys for example, an alloy of 55-60 atom % of Ni, 15-20 atom % of Mo, 6 atom % of Fe, 12-16 atom % of Cr, and 5 atom % of W.
  • Ni-Mo-Fe-Cr-Cu alloys for example, an alloy of 60 atom % of Ni, 5 atom % of Mo, 8 atom % of Fe, 21 atom % of Cr, 3 atom % of Cu, 1 atom % of Si, 1 atom % of Mn, and 1 atom % of W; and an alloy of 44-47 atom % of Ni, 5.5-­7.5 atom % of Mo, 21-23 atom % of Cr, 0.15 atom % of Cu, 1 atom % of Si, 1-2 atom % of
  • a magnetooptical recording film having a reflection film comprising aluminum, copper or gold
  • a magnetooptical recording film having a reflection film described herein has an excellent C/N ratio.
  • the refleciton film proposed herein serves to enhance the resistance to oxidation of the magnetooptical recording film, and thus, provides a magnetooptical recording medium capable of maintaining an excellent relisbility for a prolonged period of time.
  • Preferred reflection films comprise a nickel alloy having a thermal conductivity of not higher than 2J/cm.sec.K, preferably not higher than 1J/cm.sec.K.
  • reflection films composed of a Ni-Cr alloy comprising 30-99 atom % of Ni and 1-70 atom % of Cr, in particular 70-95 atom % of Ni and 5-30 atom % of Cr.
  • a reflection film composed of a metal or alloy, in particular a nickel alloy having a reduced thermal conductivity and an increased reflectance is used according to the invention, a large Kerr-rotation angle and a higher reflectance can be realized even with a thinner magnetooptical recording film.
  • the thickness of the reflection film 4 may be normally from 100 to 4000 ⁇ , preferably from 200 to 2000 A.
  • the total thickness of the magnetooptical recording film 3 and the reflection film 4 may be normally form 300 to 4600 ⁇ , and preferably from 350 to 2400 ⁇ .
  • the magnetooptical recording medium 1 according to the invention may provided with an enhancing film 5 between the substrate 2 and the magnetooptical recording film 3, and further with another enhancing film 5 between the magnetooptical recording film 3 and the reflection film 4.
  • the enhancing film 5 serves to enhance the sensitivity of the magnetooptical recording medium 1 according to the invention and also serves to protect the magnetooptical recording film 3. Any transparent film having a refractive index larger than that of the substrate can be used herein as the enhancing film.
  • the enhancing film may be composed of ZnS, ZnSe, CdS, Si3N4, SiNx, (0 ⁇ x ⁇ 4/3), Si and AlN. Of these, Si3N4 and SiNx are preferred from the stand point of anti-­crack properties.
  • the thickness of the enhancing film may be normally from 100 to 1000 ⁇ and preferably from 300 to 850 ⁇ .
  • the substrate is preferably composed of a copolymer [A] as noted below.
  • the substrate 2 is preferably composed of a random copolymer of ethylene and at least one cycloolefin of the general formula [I] or [II], said copolymer having an intrinsic viscosity [ ⁇ ] of from 0.05 to 10 dl/g as measured in decalin at a temperature of 135 o C., and a softening temperature (TMA) of at least 70 o C.
  • TMA softening temperature
  • the component derived from the cycloolefins of the general formulas [I] and [II] is present in the form of recurring units as represented by the following general formulas [III] and [IV], respectively.
  • n and m each is 0 or a positive integer
  • l is an integer of at least 3
  • R1 through R12 each represents a hydrogen or halogen atom or a hydrocarbon group.
  • the random copolymer [A] comprises a first component derived from ethylene and a second component derived from at least one cycloolefin of the general formula [I] or [II], as the essential constituent components, if desired, it may further comprise a third component derived from at least one other copolymerization monomer in an amount of up to an equimolar to that of the first component contained in the copolymer.
  • Monomers which can be used to form the third component include, for example, alpha-olefins having from 3 to 20 carbons atoms such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-­hexadecene, 1-octadecene and 1-eicocene.
  • alpha-olefins having from 3 to 20 carbons atoms such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-­hexadecene, 1-octadecene and 1-eicocene.
  • the recurring units (a) derived from ethylene are present in an amount of from 40 to 85 % by mole, preferably from 50 to 75 % by mole, while the recurring units (b) of the general formula [III] or [IV] derived from the cycloolefin or cycloolefins are present in am amount of from 15 to 60 % by mole, preferably from 25 to 50 % by mole, and these recurring units (a) and (b) are arranged in the copolymer [A] substantially at random.
  • the fact that the copolymer [A] is completely soluble in decalin at a temperature of 135 o C. indicates that it is substantially linear and free from a gel-forming cross-linked structure.
  • the copolymer [A] has an intrinsic viscosity [ ⁇ ] of from 0.05 to 10 dl/g, preferably form 0.08 to 5 dl/g, as measured in decalin at a temperature of 135 o C.
  • the softening temperature (TMA) of the copolymer [A], as measured by a thermal mechanical analyzer is at least 70 o C., preferably from 90 o to 250 o C., and more preferably from 100 o to 200 o C.
  • the copolymer [A] has a glass transition temperature (Tg) of normally from 50 o to 230 o C, and preferably from 70 o to 210 o C.
  • the crystallinity of the copolymer [A], as measured by X-ray diffractomery is normally from 0 to 10 %, preferably from 0 to 7 %, and more preferably from 0 to 5 %.
  • the magnetooptical recording medium may be prepared by depositing a magnetooptical recording film having a predetermined composition on a substrate by a known sputtering process or electron beam evaporation process, wherein the substrate is maintained at about room temperature, and use is made of a composite target with chips of elements constituting the magnetooptical recording film in the predetermined proportions or an alloy target having the predetermined composition.
  • the substrate may be fixed, or may rotates on its axis or may rotates on its axis while revolving. A reflection film is then formed on the so deposited magnetooptical recording film by the similar procedure.
  • the magnetooptical recording medium as illustrated above may be prepared at room temperature, and the magnetooptical recording film as formed are not always in need of such a heat treatment as annealing for the purpose allowing the magnetooptical recording film to have an easy axis of magnetization perpendicular to the film.
  • an amorphous alloy thin film can also be formed on a substrate while heating the substrate to 50-600 o C, or while cooling the substrate to -50 o C.
  • biasing a substrate is also possible so that the substrate comes to have a negative potential.
  • ions of an inert gas such as argon accelerated in the electric field will hit not only target substance but also a magnetooptical recording film being formed and consequently a magnetooptical recording film having further enhanced characteristics may be frequently obtained.
  • the magnetooptical recording medium comprising a substrate, a magnetooptical recording film (I) which is a thin film of an amorphous alloy or a specified composition and a reflection film (II) composed of a metal or alloy having a thermal conductivity of not higher than 2 J/cm.sec.K., in which said films are laminated on a substrate in this order, has excellent resistance to oxidation, and in consequence, it is advantageous in that its magnetooptical recording film (I) can be thin; a warp of the medium and film cracking are not liable to occur; it has a high C/N ratio; in addition to excellent magnetooptical characteristics its coercive force and Kerr-rotation angle do not substantially change with time; and it has an increased reflectance.
  • a magnetooptical disc was produced by successively laminating on a disc substrate of an ethylene/­tetracyclododecene copolymer having an ethylene content of 60% by mole, a tetracyclododecene content of 40 % by mole, a softeninig temperature (TMA) of 155 o ., an intrinsic viscosity [ ⁇ ] of 0.45 dl/g and a crystallinity of 0% as measured by X-ray diffractometry, according to the sputtering process a film of ZnS having a thickness of 600 ⁇ as an enhancement layer, a film of Pt20 Tb32 Fe36 Co12 having a thickness of 200 ⁇ as a magnetooptical recording layer, and a film of Fi having a thickness of 200 ⁇ as a reflective layer.
  • TMA softeninig temperature
  • a magnetooptical disc was produced by successively laminating on the same disc substrate as used in Example 1 according to the sputtering process a film of ZnS having a thickness of 600 ⁇ as an enhancement layer, a film of Pt20 Tb32 Fe36 Co12 having a thickness of 200 ⁇ as a magnetooptical recording layer, and a film of Al (heat conductivity 2.37 J/cm.sec.K) having a thickness of 200 ⁇ as a reflective layer.
  • Example 1 Making a comparison between Example 1 and Comparative Example 1, it is understood that the laser power necessary for recording in the latter example is more than two times that in the former example, even though the values of C/N obtained in both examples are at the same level.
  • Example 1 was repeatd except that the film of Ti used had a thickness of 400 ⁇ . As the result, the optimum laser power was 3.1 mW and C/N was 44 dB.
  • Comparative Example 1 was repeatd except that the film of Al used had a thickness of 400 ⁇ . As the result, no recording could be performed even when the laser power increased up to 8.0 mW.
  • Example 1 was repeatd except that the magnetooptical recording layer used had a composition of Pt20 Tb32 Fe26 Co22. As the result, the optimum laser power was 3.9 mW and C/N was 44 dB.
  • Example 1 was repeatd except that the magnetooptical recording layer used had a composition of Pt20 Tb32 Fe22 Co26. As the result, the optimum recording laser power was 5.8 mW, and C/N was 46 dB.
  • Example 1 was repeatd except that a film of Pt having a thickness of 200 A was used as the reflective layer. As the result, the optimum recording laser power was 3.5 mW and C/N was 45 dB.
  • Example 1 was repeatd except that a film of Pt having thickness of 400 ⁇ was used as the reflective layer.
  • Example 1 was repeatd except that a film of Pd having a thickness of 200 ⁇ was used as the reflective layer. As the result, the optimum recording laser power was 3.5 mW and C/N was 45 dB.
  • a magnetooptical disc was produced by successively laminating on the same disc substrate as used in Example 1 according to the sputtering process a film of SiNx having a thickness of 700 ⁇ as an enhancement layer, a film of Pt18 Tb34 Fe38 Co10 having a thickness of 300 ⁇ as a magnetooptical recording layer, and a film of Ni80 Cr20 having a thickness of 700 ⁇ as a reflective layer.
  • the optimum recording laser power was 3.5 mW and C/N was 50 dB (reproducing laser power was 1.0 mW).
  • Example 8 Following substantially the same procedure as described in Example 8, there were produced magnetooptical discs, whose magnetooptical layer and reflective layer had the composition and thickness as indicated in Table 5. The discs thus obtained were evaluated in the same manner as in Example 8 to obtain the results as shown in Table 5.
  • Magnetooptical recording media prepared in the following examples were evaluated in the manner mentioned below.
  • test specimens 10 x 10 x 0.5 mm, molded from polymers shown in Table 2 by press molding was measured, wherein no load was placed on the specimen or stress was applied to the specimen by suspending a weight of 50 g, 100 g or 200 g therefrom, and an optical elasticity constant of the specimen was obtained from the relation between the double refractive index obtained and stress applied.
  • a photoelasticity constant was measured in an ethylene/tetracyclododecene copolymer containing 60 mol % of ethylene (by means of 13C-NMR, it was confirmed that tetracyclododecene in the copolymer had a structure of polymethyl methacrylate (T10-10, a product of a Kyowa Gas Kagaku Kogyo) and polycarbonate (AD-5503, a product of Teijin Kasei), both of which are starting polymers for conventional opticaldiscs.
  • T10-10 polymethyl methacrylate
  • AD-5503 a product of Teijin Kasei
  • test specimens molded into the form of disc were measured at a distance of radius r mm from the center of the specimen at the time when the angle of illumination of laser was shifted diagonally 10 o by 10 o , assuming the vertical direction as 0 o .
  • Disc substrates of 130 mm in diameter were molded respectively from the ethylene/tetracyclododecene copolymer (PO), which were used in Referential Example 1.
  • PO ethylene/tetracyclododecene copolymer
  • a film of each compound as shown in Table 8 was successively formed by the sputtering process to a thickness of 500 ⁇ as an enhancement layer, a magnetooptical recording layer comprising TbFe to a thickness of 1000 ⁇ , and an enhancement layer to a thickness of 500 ⁇ .
  • the mangetoopticl recording media thus obtained were allowed to stand for 7 days at 70 o C and 85 % RH, subjected to a 7-day heat cycle test wherein the media were allowed to stand alternately at -20 o C for 2 hours and at +60 o C for 2 hours to measure coercive force (Hc) thereof.
  • Table 8 Example Magnetooptical recording medium Change in Hc(Koe) Substrate Interlayer 70 o C, 85% RH Heat cycle 16 PO Si3N4 No change No change 17 PO CdS No change No change 18 PO ZnSe No change No change 19 PO ZnS No change 20 PO Si No change No change 21 PO AIN No change No change
  • the magnetooptical recording media of the present invention maintain the initial coercive force quite stably.
EP88906911A 1987-08-08 1988-08-08 Photomagnetisches speichermedium Expired - Lifetime EP0331737B1 (de)

Applications Claiming Priority (7)

Application Number Priority Date Filing Date Title
JP198713/87 1987-08-08
JP62198713A JP2633572B2 (ja) 1987-08-08 1987-08-08 光磁気記録体
JP62207629A JPS6450256A (en) 1987-08-20 1987-08-20 Magneto-optical recording medium
JP207629/87 1987-08-20
JP335554/87 1987-12-28
JP33555487A JPH01179241A (ja) 1987-12-28 1987-12-28 光磁気記録媒体
PCT/JP1988/000785 WO1989001687A1 (en) 1987-08-08 1988-08-08 Photomagnetic recording medium

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EP0331737A1 true EP0331737A1 (de) 1989-09-13
EP0331737A4 EP0331737A4 (en) 1991-07-03
EP0331737B1 EP0331737B1 (de) 1996-06-05

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AT (1) ATE139052T1 (de)
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WO (1) WO1989001687A1 (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0406823A2 (de) * 1989-07-05 1991-01-09 Mitsui Petrochemical Industries, Ltd. Magnetooptische Aufzeichnungsmedien
EP0449183A2 (de) * 1990-03-27 1991-10-02 Teijin Limited Magnetooptisches Aufzeichnungsmedium
EP0454858A1 (de) * 1989-11-10 1991-11-06 Mitsubishi Chemical Corporation Magnetooptisches aufzeichnungsmedium
EP0503607A2 (de) * 1991-03-14 1992-09-16 TDK Corporation Magneto-optisches Aufzeichnungsmedium
US5233575A (en) * 1989-11-10 1993-08-03 Mitsubishi Kasei Corporation Magneto-optical recording medium
US5700567A (en) * 1991-03-14 1997-12-23 Tdk Corporation Magneto-optical recording medium

Families Citing this family (3)

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CN1018304B (zh) * 1988-10-17 1992-09-16 三井石油化学工业株式会社 磁光记录介质
CA2014751C (en) * 1989-10-19 1996-01-23 Kunihiko Mizumoto Magnetooptical recording media
CN108425080B (zh) * 2018-02-27 2020-04-28 南方科技大学 单质非晶钯及其制备方法和用途

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EP0128960A1 (de) * 1982-12-23 1984-12-27 Sony Corporation Thermomagnetisches optisches aufzeichnungs-/wiedergabeverfahren
EP0192256A2 (de) * 1985-02-21 1986-08-27 Sharp Kabushiki Kaisha Magnetooptischer Informationsträger
GB2175160A (en) * 1985-05-09 1986-11-19 Kokusai Denshin Denwa Co Ltd Magneto-optical recording medium
EP0229292A1 (de) * 1985-12-05 1987-07-22 Hitachi Maxell Ltd. Optisch-magnetischer Aufzeichnungsträger
JPS639040A (ja) * 1986-06-30 1988-01-14 Matsushita Electric Ind Co Ltd 光学情報記録媒体
EP0310680A1 (de) * 1987-04-17 1989-04-12 Mitsui Petrochemical Industries, Ltd. Photomagnetische speichermembran
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EP0128960A1 (de) * 1982-12-23 1984-12-27 Sony Corporation Thermomagnetisches optisches aufzeichnungs-/wiedergabeverfahren
EP0156464B1 (de) * 1984-02-03 1996-05-22 Mitsui Petrochemical Industries, Ltd. Statistische Copolymere
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GB2175160A (en) * 1985-05-09 1986-11-19 Kokusai Denshin Denwa Co Ltd Magneto-optical recording medium
EP0229292A1 (de) * 1985-12-05 1987-07-22 Hitachi Maxell Ltd. Optisch-magnetischer Aufzeichnungsträger
JPS639040A (ja) * 1986-06-30 1988-01-14 Matsushita Electric Ind Co Ltd 光学情報記録媒体
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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0406823A2 (de) * 1989-07-05 1991-01-09 Mitsui Petrochemical Industries, Ltd. Magnetooptische Aufzeichnungsmedien
EP0406823B1 (de) * 1989-07-05 1997-10-22 Mitsui Petrochemical Industries, Ltd. Magnetooptische Aufzeichnungsmedien
EP0454858A1 (de) * 1989-11-10 1991-11-06 Mitsubishi Chemical Corporation Magnetooptisches aufzeichnungsmedium
EP0454858A4 (en) * 1989-11-10 1993-02-24 Mitsubishi Kasei Corporation Magnetooptical recording medium
US5233575A (en) * 1989-11-10 1993-08-03 Mitsubishi Kasei Corporation Magneto-optical recording medium
EP0449183A2 (de) * 1990-03-27 1991-10-02 Teijin Limited Magnetooptisches Aufzeichnungsmedium
EP0449183A3 (en) * 1990-03-27 1992-02-26 Teijin Limited Magneto-optical recording medium
US5560998A (en) * 1990-03-27 1996-10-01 Teijin Limited Magneto-optical recording medium
EP0503607A2 (de) * 1991-03-14 1992-09-16 TDK Corporation Magneto-optisches Aufzeichnungsmedium
US5700567A (en) * 1991-03-14 1997-12-23 Tdk Corporation Magneto-optical recording medium
EP0503607B1 (de) * 1991-03-14 1999-07-21 TDK Corporation Magneto-optisches Aufzeichnungsmedium

Also Published As

Publication number Publication date
DE3855347T2 (de) 1996-10-31
EP0331737B1 (de) 1996-06-05
DE3855347D1 (de) 1996-07-11
WO1989001687A1 (en) 1989-02-23
EP0331737A4 (en) 1991-07-03
ATE139052T1 (de) 1996-06-15

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